Generally, EDM apparatus can be divided into two types, die-sinking EDM machines and wire-cut EDM machines. A die-sinking EDM machine uses a 3-dimensional tool electrode with a dielectric fluid, such as, for example, an aqueous solution containing kerosene or a high molecular weight compound, in the gap between the electrode and the workpiece, as the machining medium. It machines the workpiece by applying voltage to that gap and generating an electrical discharge across the gap.
On the other hand, a wire-cut EDM machine uses wire made from such material as brass or tungsten of a diameter of 0.02 to 0.03 mm as the tool electrode. It machines the workpiece by running the wire in juxtaposition with the workpiece between a pair of wire guides. It generally uses deionized water or a kerosene based fluid as the dielectric fluid that is present between the wire and the workpiece.
In finish-machining, it is known that using a dielectric fluid with, for example, finely powdered polycrystalline silicon, mixed in it, will provide a good surface roughness on the workpiece and will improve machining stability. British Patent No. 828,336 and U.S. Pat. Nos. 4,392,042 and 4,952,768 disclose the use of this sort of fluid.
If this fluid is used in a wire-cut EDM machine, it could affect the travel of the wire by, for example, powder entering the rotating parts in the work tank, such as the bearings in the rollers provided along the wire conveying route, and, as a result, causing an undesirable effect on the machining. Furthermore, if the powder enters the movable wire guides or into the wire guide assemblies containing the movable electricity feeding elements which supply electricity to the wire, it could hinder the movements of those guides and elements. Also, much labor is required to remove the powder that remains in the wire conveying mechanism and guide assemblies when the machining work is finished.